Vapour phase hydration studies of simulant Magnox waste glass have been undertaken at 200°C, over periods of 5 – 25 days. Electron microscopy studies reveal a thin uniform hydration layer (∼10 μm thick) on 5, 10 and 25 day specimens. The formation of isolated surface alteration products occurs between 5 and 10 days at 200°C. The formation of extensive surface alteration products, in the form of a magnesium sodium aluminosilicate, is observed only in the case of the 25 day specimen. The significance of these observations in the context of the composition of Magnox waste glass, is discussed.